OK, time to drag out my 1988 GTA and finish up the engine repairs. I had the original 305 rebuilt over the winter. It was bored .030", heads refreshed and a 1993 LT1 cam installed,everything else internal is stock. No headers, Magnaflow cat and stock exhaust. My question is can I use my GM 1.6 roller rocker arms and what are the specs for the base timing and minimum idle speed? Thanks.

 

It depends on what was done to the heads. Normally the stock heads and valve springs will support around .470" lift. Thats a stock TPI cam with 1.6 rockers, or an LT1 cam with 1.5 rockers, but not both. If you used different springs that are set up to handle the lift of an LT1 cam with 1.6 rockers, then it should work.

Stock TPI initial timing is 6* BTDC, and the idle is around 650 RPMs.

 

Thanks for the reply Kevin. The springs/retainers installed by the machine shop, are Manley's and are capable of the extra lift, I planned on using the 1.6 rockers since I already had them. Heads were not ported, etc. Car is an automatic (700r4). Should the min idle speed be set to the book numbers ( 400 rpm for a 305)? I have read that the adjustment is supposed to be done with the car in gear, but the shop manual states neutral. Also, is your suggested RPM just done with the car idling and turning the adjustment screw, rather than going thru the detailed procedure as outlined in the manual?

 

400 rpm seems low... i always thought it was 500-550 for idle in drive and 600-650 in park... but those manely springs and retainers should be good till near 510 lift.. i have manely springs retainers and screw in studs on my l98 heads and they clear the lift for my gm hotcam but with this cam i had to raise my idle to around 800 to keep it from stalling out... so i would put those 1.6 rockers in.... does your heads have screw in studs or press in.... press in type sucks and are in danger of coming out with any bigger cam and revving the engine higher....

 

I think that the 400 is minimum idle speed, but I could be mistaken. Once that is set, you plug back in the IAC motor, and it should take it the rest of the way up to where it needs to me.

 

Thanks for the help guys. I decided to contact the tuner I have used in the past and see if he recommends a reflash to the prom (presently not installed with this engine combo). He states that you set the timing to the factory spec (6 degrees BTDC) and adjust the idle screw to get the IAC steps to be between 10-60 with the engine running at the "desired idle" number that is controlled by the ECM. Will wait for his response on a reflash and go from there.